-LRB- CNN -RRB- -- Researchers believe the number of children who have an autism spectrum disorder -LRB- ASD -RRB- is much higher than previously believed , according to a new study published Monday in the American Journal of Psychiatry .

By looking at a total population sample in South Korea , the study authors estimate that 1 in 38 children in the country -- or 2.64 % -- has some form of autism . The approach is a new one . Previously , researchers have examined only children known to have the neurological disorder or at high risk of developing it .

The study authors predicted that if similar studies were conducted in other countries , the prevalance estimates would also go up .

The research also led the study authors to believe that more girls than previously thought fall under the autism umbrella .

What is autism ?

In the United States , the most recent estimates from the Centers for Disease Control and Prevention -LRB- CDC -RRB- for autism prevalence are about 1 % or 1 in 110 children , based on population studies in a select number of areas around the country .

In this new study , researchers looked at all 55,000 school children in a large metropolitan community of Seoul , which they say is representative not only of South Korea , but also many other developed nations .

According to the study , researchers began with 55,266 7 - to 12-year-old students . Parents and teachers were asked to fill out an autism screening questionnaire . Parents of 23,234 of the children in the regular school system responded . All 294 children already enrolled in special education or on the disability registry were considered to have tested positive for an autism spectrum disorder .

From the initial assessments , 1,214 students screened positive for some form of autism . Only 286 went on to get a full clinical evaluation , of which 201 were diagnosed with some form of autism . Using mathematical algorithms , researchers estimate 1 in 38 children in South Korea have an autism spectrum disorder .

`` Are we surprised ? Yes , '' said Dr. Young Shin Kim , lead author of the study and assistant professor at the Child Study Center at the Yale School of Medicine . Kim said the prevalence estimates in the study , which happened to take place in South Korea , are higher than previous estimates elsewhere , including but not exclusively the United States .

Kim said she believes if more studies like this are done in other countries , they , too , will find an autism rate of 2-3 % , while acknowledging that more research needs to be done to validate the study results .

In depth autism coverage on The Chart

The study does n't mean that suddenly many more children have autism , Kim said . Instead , she suggests `` they have been there all along but they were not counted in previous prevalence studies , '' and that `` two-thirds are in the community unrecognized and untreated . ''

Roy Richard Grinker , a cultural anthropologist at George Washington University and one of the co-authors of the study , said he thinks the study 's estimates are `` surprising '' but he does n't think they are alarming . What these estimates tell us , he said , is that `` autism is more common than we think it is . ''

Autism and communication

Grinker said he would compare the situation in South Korea to where the United States was 20 years ago , as far as autism awareness goes . He said when the study began in 2005 , South Koreans believed that autism was rare in their country . He cited one South Korean official who he said estimated the prevalence of autism to be about 1 in 100,000 .

At that same time , the CDC estimated autism prevalence to be about 1 in 150 children and Australian researchers believed it to be around 1 in 160 children .

Since then , new research has led to a 1 in 110 prevalence estimate .

When asked about the newest estimates , Dr. Marshalyn Yeargin-Allsopp , chief of the Developmental Disabilities Branch of the National Center on Birth Defects and Developmental Disabilities at the CDC , said , `` We 've always said that what we report is an underestimate . ''

She said there are different ways to determine prevalence and that the CDC is considering a total population study of autism , but that it is not yet under way .

Vanderbilt University 's director of the Treatment and Research Institute for Autism Spectrum Disorders -LRB- TRIAD -RRB- , believes the new data adds to what 's already been known about ASD in other parts of the world -- that autism is not rare .

But Dr. Zachary Warren , who did not participate in the study , also said , `` In the current study the authors sampled from a population , noted that many folks from this sample did not participate , and performed diagnostic evaluations on a relatively small number of children . As such , these concerns suggest interpreting the 2-3 % prevalence rate reported with significant caution as it may in fact be an overestimate related to how they studied this specific community in Korea . ''

Dr. Max Wiznitzer , a pediatric neurologist at Rainbow Babies & Children 's Hospital in Cleveland , Ohio , said the results of this study -LRB- which he also was n't part of -RRB- , suggest that what the numbers tell us is `` that -LRB- many -RRB- children in this district in Korea have difficulties with social/communications skills . ''

`` We have to be careful not to confuse them with other conditions that can also cause problems in these realms like ADHD and social anxiety disorders , '' he said .

What makes Monday 's study different from other autism studies is that researchers sought out children in regular schools . According to the researchers , few children in South Korea are put in special education classes . Grinker said about 10-12 % of school children from K-12 classes receive some form of special needs education , but that in Korea that figure is far lower , maybe under 1 % . He attributes that to a law that mandates inclusion , which makes it difficult to provide special education .

Also , children in regular schools in Korea are in school for up to 12 hours a day , with highly structured , large classrooms , and few opportunities for socialization . Many of the children who were identified with an autism spectrum disorder through this study were found to have a higher IQ , but had poor socialization skills , one of the hallmarks of autism .

`` I think many children with autism can do well in that highly structured situation and may not get flagged as having a particular problem , '' Grinker said .

This may explain why many children with autism in South Korea may go unnoticed and may explain a significant difference with children in the United States .

Dr. Geraldine Dawson , chief science officer of the advocacy group Autism Speaks , which funded part of the study , believes the most important finding is that the research shows that using `` the comprehensive sampling approach ... has the potential to yield an autism prevalence estimate that exceeds previous estimates . ''

Grinker believes the most important message from the study is not the numbers , but that it suggests that `` autism is more common than we previously thought and that , if we look hard enough , cases will be found and these children need treatment so they can thrive . ''

Dawson also believes that the study clearly confirms that autism is a significant global public health concern that transcends cultural , geographic and ethnic boundaries .

It also shows that it 's possible to translate and adopt screening and diagnostic approaches developed in English-speaking countries to effectively assess prevalence in other countries .

Autism Speaks is funding similar research in India , South Africa , Mexico and Taiwan , Dawson said .

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A new study estimates 1 in 38 South Korean children has some form of autism

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The estimate is based on a new approach to autism research

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Study authors call the findings `` surprising ''

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The study was published in the American Journal of Psychiatry